Aliphatic terminal alkenes (or alpha-olefins) are produced in metric megaton amounts each year, and these chemical feedstocks are starting materials for the preparation of many classes of organic compounds. The value-added component of catalytic intermolecular reactions of these alkenes, such as Ziegler-Natta oligomerization, the Heck reaction, and cross-metathesis, is especially high because they convert an inexpensive raw material into a more highly functionalized compound or polymer with concomitant formation of one or more carbon-carbon bonds.
Allylic alcohols are important building blocks commonly used in the synthesis of natural products and other complex molecules and polymers. However, current synthetic methods known to the inventors have not been able to incorporate alpha-olefins in the synthesis of allylic alcohols. Previous studies typically have involved metal-catalyzed, intermolecular reductive coupling reactions of aldehydes with alkynes, 1,3-dienes, allenes, enoate esters, enones, and enals. In these examples, a reactive π-bond has been, in effect, converted to an anion equivalent by a reductive process. Because the less reactive π-bond of an alpha-olefin may not as easily be activated in this manner, catalytic intermolecular coupling (e.g., reductive or otherwise) of these alkenes and aldehydes has not been achieved. While catalytic carbonyl-ene reactions between alpha-olefins and aldehydes provide homoallylic alcohols, there is no method known to the inventors for joining these two building blocks to provide allylic alcohols. Nickel-promoted, intramolecular alkene-aldehyde reductive coupling was recently described (Ogoshi, S.; Oka, M.-a.; Kurosawa, H. J. Am. Chem. Soc. 2004, 126, 11802-11803), but this process required a stoichiometric amount of nickel and was not effective in intermolecular cases.
Accordingly, improved methods are needed.